/Engine/Source/Runtime/Engine/Classes/Engine/Polys.h
Split with plane quickly for in-game geometry operations. Results are always valid. May return sliver polys.
int32 SplitWithPlaneFast ( const FPlane & Plane, [FPoly](API\Runtime\Engine\Engine\FPoly) * FrontPoly, [FPoly](API\Runtime\Engine\Engine\FPoly) * BackPoly ) const